Attempts to blend polypropylene and polyamide have been made to obtain a resin material having the water resistance of polypropylene, especially crystalline polyolefins, and the mechanical properties, heat resistance, and dyeability of polyamide. This object is not achieved by a mere blending of polypropylene and polyamide by melt-mixing. Mere blending provides a mixture which is subject to phase separation and is poor in surface gloss and mechanical properties, because polypropylene and polyamide mix poorly. To overcome this disadvantage, a blend of polypropylene and polyamide is incorporated with maleic anhydride-modified polypropylene.
The addition of the modified polypropylene alone is not sufficient to improve physical properties such as impact resistance and surface properties. therefore, there was proposed the incorporation of a low crystalline or amorphous polymer modified with an unsaturated carboxylic acid anhydride. For example, there is disclosed a composition composed of a polyamide and a modified product of a mixture of crystalline polyolefin and low-crystalline or amorphous ethylene-.alpha.-olefin copolymer (Japanese Patent Laid-open No. 8246/1982); a compound composed of a modified polypropylene, a polyamide, a modified product of low-crystalline or amorphous ethylene-.alpha.-olefin copolymer, and an inorganic filler (Japanese Patent Laid-open No. 53550/1985); a composition composed of polypropylene, polyamide and/or polyester, a modified product of low-crystalline or amorphous ethylene-.alpha.-olefin copolymer, and an inorganic filler (Japanese Patent Laid-open No. 76548/1985); and a composition composed of polypropylene, polyamide, and low-crystalline or amorphous modified propylene-.alpha.-olefin copolymer (Japanese Patent Laid-open No. 110740/1985).
On the other hand, for the improvement of dispersibility of polyamide into polyolefin and for the improvement of dyeability of polyolefin, there is proposed a composition composed of acid-modified polypropylene with a metal atom bond, polyamide, and polyolefin (Japanese Patent Laid-open No. 74143/1984).
Conventional compositions are improved in impact resistance by incorporating a low-crystalline or amorphous copolymer or an acid-modified product thereof. However, they have no satisfactory surface gloss. Compositions incorporated with acid-modified polypropylene with a metal atom bond are improved in dispersibility but not satisfactorily improved in impact resistance.